SYNTHESIS OF ARISTOTELIA-TYPE ALKALOIDS .12. TOTAL SYNTHESIS OF (-)-TASMANINE - STEREOELECTRONIC FACTORS THAT CONTROL THE REARRANGEMENT OF 3H-INDOL-3-OL DERIVATIVES TO OXINDOLES (= 1,3-DIHYDRO-2H-INDOL-2-ONES)OR TO PSEUDOINDOXYLS (= 1,2-DIHYDRO-3H-INDOL-3-ONES)
R. Guller et Hj. Borschberg, SYNTHESIS OF ARISTOTELIA-TYPE ALKALOIDS .12. TOTAL SYNTHESIS OF (-)-TASMANINE - STEREOELECTRONIC FACTORS THAT CONTROL THE REARRANGEMENT OF 3H-INDOL-3-OL DERIVATIVES TO OXINDOLES (= 1,3-DIHYDRO-2H-INDOL-2-ONES)OR TO PSEUDOINDOXYLS (= 1,2-DIHYDRO-3H-INDOL-3-ONES), Helvetica Chimica Acta, 76(5), 1993, pp. 1847-1862
The oxidative transformation of (+)-aristoteline ((+)-5) into its meta
bolites, the recently synthesized indole alkaloids (-)-serratoline ((-
)-6), (+)-aristotelone ((+)-2), and (-)-alloaristoteline ((-)-22), was
investigated in more detail. It was demonstrated that the diastereofa
ce selectivity of the reaction of(+)-5 with 3-chloroperbenzoic acid ca
n be altered by variation of the solvent as well as by addition of CF3
COOH. The chemoselectivity of the 1,2-rearrangement of the intermediat
e 3H-indol-3-ol derivatives could be controlled as follows: treatment
of 3H-indol-3-ols with aqueous polyphosphoric acid led to the pseudoin
doxyl (= 1,2-dihydro-3H-indol-3-one) derivatives, whereas an analogous
treatment of the corresponding 0-benzoates furnished exclusively the
corresponding, constitutionally isomeric 2-oxindole (= 1,3-dihydro-2H-
indol-2-one) products. Exploitation of these and related findings led
to efficient total syntheses of the Aristotelia alkaloid (-)-tasmanine
((-)-1) and of the corresponding unnatural epimer (+)-12, as well as
of the two pseudoindoxyls (+)-aristotelone ((+)-2) and (-)-2-epiaristo
telone((-)-11). All these transformations were carried out with synthe
tic (+)-aristoteline ((+)-5) as the single indole alkaloid precursor.